<!DOCTYPE html>
<html>

	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>

	<body>
		<input id="num" />
		<br />
		<input type="button" value="1" onclick="one()" />
		<input type="button" value="2" onclick="two()" />
		<input type="button" value="3" onclick="three()" />
		<input type="button" value="c" onclick="qingChu()" />
		<input type="button" value="+" onclick="jia()" />
		<input type="button" value="-" onclick="jian()" />
		<input type="button" value="*" onclick="cheng()" />
		<input type="button" value="/" onclick="chu()" />
		<script>
			var one = function() {
				num.value = num.value + "1";
			};
			var two = function() {
				num.value = num.value + "2";
			};
			var three = function() {
				num.value = num.value + "3";
			};
			var qingChu = function() {
				num.value =  "";
			};
			
		</script>

	</body>

</html>